I would advocate for using a `!` on the end of whatever we pick to signify it does something "dangerous" (e.g. exception) just as a warning for users. On Wed, Jan 14, 2026 at 9:35 AM mame (Yusuke Endoh) via ruby-core < ruby-core@ml.ruby-lang.org> wrote:
Issue #13683 has been updated by mame (Yusuke Endoh).
`Enumerable#sole` is a method that should only be used when the Enumerable has only one element. Using it in other cases (0 or 2+ elements) is considered a bug, or literally "exceptional", so raising an exception makes perfect sense.
In the dev meeting, when we consider the name `Enumerable#one!`, I briefly mentioned `Enumerable#one`, a moderate variant that returns `nil` instead of raising an exception. But no one seriously considered it because we can find no use case for it.
---------------------------------------- Feature #13683: Add strict Enumerable#single https://bugs.ruby-lang.org/issues/13683#change-116111
* Author: dnagir (Dmytrii Nagirniak) * Status: Feedback ---------------------------------------- ### Summary
This is inspired by other languages and frameworks, such as LINQ's [Single]( https://msdn.microsoft.com/en-us/library/bb155325%28v=vs.110%29.aspx) (pardon MSDN reference), which has very big distinction between `first` and `single` element of a collection.
- `first` normally returns the top element, and the developer assumes there could be many; - `single` returns one and only one element, and it is an error if there are none or more than one.
We, in Ruby world, very often write `fetch_by('something').first` assuming there's only one element that can be returned there.
But in majority of the cases, we really want a `single` element.
The problems with using `first` in this case:
- developer needs to explicitly double check the result isn't `nil` - in case of corrupted data (more than one item returned), it will never be noticed
`Enumerable#single` addresses those problems in a very strong and specific way that may save the world by simply switching from `first` to `single`.
### Other information
- we may come with a better internal implementation (than `self.map`) - better name could be used, maybe `only` is better, or a bang version? - re-consider the "block" implementation in favour of a separate method (`single!`, `single_or { 'default' }`)
The original implementation is on the ActiveSupport https://github.com/rails/rails/pull/26206 But it was suggested to discuss the possibility of adding it to Ruby which would be amazing.
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